1. Field of the Invention
The present invention is directed toward contact lens disinfecting apparatus, and more particularly contact lens disinfecting apparatus which feature the use of a positive temperature coefficient (PTC) heater element for imparting the proper disinfecting heat to the contact lenses.
2. Description of the Prior Art
Contact lens disinfecting units which are in common use today generally include a lens carrying case that is placed in intimate engagement with a heat dispersing plate. Close proximity to an electrically energized heater provides heat to the plate which in turn heats the contact lens carrying case by conduction and the lenses carried within to a predetermined temperature for a period of time sufficient to properly disinfect the lenses. When this period of time elapses the disinfecting unit shuts off and the current flow to the heater is terminated. The contact lens carrying case, after being allowed to cool for a period of time may then be removed and the contact lenses inserted in the user's eyes.
Generally, then, many of the contact lens disinfectors presently known apply electric current to a heating element which heats a heat dispersing plate, which in turn applys heat to a contact lens carrying case. The electrical current is generally controlled by a thermostatic switch which is used to determine when the heater reaches a certain preselected temperature. Once the temperature of the heater reaches the preselected point, the thermostatic switch opens, thereby breaking the flow of electrical current to the heater. At this time the contact lenses within the carrying case may have been exposed to sufficient heat for the required period of time to insure that they are properly disinfected or, the lens carrier may remain in contact with the heater for a period of time after the current is shut off to insure that proper disinfecting takes place. In some instances, the thermostatic switch may also control a light which is wired in series with the switch and in parallel with the heater. The light would be lit when the switch is closed and current is flowing to the heater. When the thermostatic switch senses that the preselected temperature has been reached, it opens shutting off the current to the heater and the light as well.
As in any electrical appliance, however, the more components used in its manufacture the greater is the chance that failure may occur in one, or more, of the components resulting in erratic behavior or complete breakdown of the unit. Also, the more components used in a product the more costly it becomes. Still further, when more components are used there is the associated risks that manufacturing difficulties will arise.
A contact lens disinfector which uses the above-mentioned thermostatic switch to control the flow of electricity to the heater suffers from the inherent possibility that the switch may fail, which in turn would cause the unit to fail. The switch could fail by either not opening or not closing. If the switch fails to open, the disinfecting unit presents a very definite hazard (in the absence of a thermal limiter fail-safe device) in that possible damage to the lenses could occur or, far more serious, fire could result. If the thermocouple switch fails to close, the unit would simply fail to operate and the user's lenses would not be properly disinfected.
Various issued U.S. patents disclose contact lens disinfectors which incorporate some, or all, of the above discussed features. U.S. Pat. Nos. 4,044,226 issued Aug. 23, 1977 to J. Kadlecik et al, 4,158,126 issued June 12, 1979 to L. J. Seitz, 4,178,499 issued Dec. 11, 1979 to J. G. Bowen, 4,235,842 issued Nov. 25, 1980 to M. D. Thomas et al and 4,242,572 issued Dec. 30, 1980 to M. D. Thomas et al, are some of these.
A number of U.S. patents have also been issued which disclose a number of ways to provide heat into food stuffs or liquids. Some of the patents exemplary of this type of warmers known to use a PTC heater are U.S. Pat. Nos. 3,720,807 issued Mar. 13, 1973 to Youn H. Ting, 3,876,861 issued Apr. 8, 1975 to J. W. Wightman et al, 3,995,141 issued Nov. 30, 1976 to D. P. Vieau et al and 4,160,152 issued July 3, 1979 to J. W. Wightman et al.